That may be. I see some of the same in 92026. What most folks seem to not understand is that if the front side (top) of a panel or of an array is (hopefully) oriented so as to have the most favorable conditions available for operation, to a 1st approx., logic and common sense might lead one to surmise that a surface oriented in the precisely opposite direction, that is, the back side of a panel or array might just have close to the worst orientation, or at least not very good. But never mind that for now. That's just my dumb country upbringing floating to the surface like the big chunks in a cess pit.
On the 80 kW sundeck: I'd guess the panels and the array are somewhat horizontal ? Or if tilted, probably something like @ 20 deg. or so ? Without going into particulars about things like diffuse surface reflection and directionality, along with forward vs. backward scattering, view factors, and a bunch of other stuff, I'll take a SWAG that the incident radiation on the underside of those panels if they are, at, say, 20 - 30 ft. off the ground, is probably not much more than 5% or so of the front side irradiance.
By way of some explanation: A thought experiment: For hours of collection, say between 0900 and 1500 hrs. solar time, a good portion of the ground (the white concrete) surface that the underside of that array will "see" with more than a very small view factor will be the ground under the array, and thus (unfortunately) be shaded - and so not much to reflect there - only diffuse reflected, some of which was itself reflected before it got to the only reflecting surface with a decent view factor. The view factors for the rest of the surroundings - for walls, other nearby surrounding buildings (and probably not as white and therefore not as reflective) etc., will be quite small, the smallness of the view factors mostly due to the high angles of incidence of the other surfaces relative to the undersurface of the array. For the white concrete under the array, if it is shaded by the array, as it must be (for most of the time and mostly during peak sun hours), that means the only solar radiation incident on the concrete under most of the array will be diffuse, with the additional penalty (to reiterate) that most or all such diffuse radiation will be comprised mostly of backscattered diffuse radiation and diffuse radiation incident as a result of already having been reflected from other probably diffuse surfaces, perhaps multiple times, weakening and scattering more with each "re"-reflection.
Additionally, since it's highly likely that most or all of the small amount of solar radiation reaching the underside of the array will be diffuse, an additional penalty will be in place. Reason: transmittance of diffuse radiation through glazing is less than for beam radiation. This is due to the higher effective (averaged) angles of incidence of the scattered, diffused light, and how, because higher angles of incidence have greater surface reflectance, less radiation is present tor transmittance.The common approximation is to take the reflectance of diffuse radiation as being appox. the same as that of beam radiation at a 60 deg. incidence angle. For most transparent materials used in solar energy applications that translates into an approx. 10% additional penalty in collected energy. That's due to increased reflection of diffurse solar radiation only.
There is also a small additional penalty to be paid due to increased panel temp. This is small, but ought to be at least considered. Say the backside enhancement does amount to a 5 % increase in incident radiation. Since, at least to a pretty good 1st approx., and from energy (heat) balance considerations, that will increase the cell temperatures by something like ~ 5% over the not bifacial temp. diff between the array and the surroundings. That will mean something like a 1 C. or so increase in panel temp., resulting in another 0.5% or so decrease in energy collected due to temp. induced efficiency decrease. That needs to be taken as a reduction to my (assumed) 5 % enhancement from back face irradiation..
Now, If the design came in at the same price with or without bifacial panels, and assuming (somewhat generously I'd respectfully submit), O. & M. and other costs are the same, I'd say consider going for the bifacial option for this non residential option. However, given the dearth of knowledge surrounding how to estimate the potential enhancement to incident radiation on the backside of panels from reflection, I'd not go for it if it cost much more than the non bifacial option without some serious work.
I'd respectfully suggest to those who think large increases in incident radiation, and thus annual output are possible from the use of bifacial panels, to understand the possibilities and constraints that are part of the reality of the situation. Large (say~ > 10 % ) increases in actual yearly output without some compromises in aesthetics or some added costs in ancillary equipment or additional design requirements are probably hard to come by, and rarely cost effective in residential situations.
On the 80 kW sundeck: I'd guess the panels and the array are somewhat horizontal ? Or if tilted, probably something like @ 20 deg. or so ? Without going into particulars about things like diffuse surface reflection and directionality, along with forward vs. backward scattering, view factors, and a bunch of other stuff, I'll take a SWAG that the incident radiation on the underside of those panels if they are, at, say, 20 - 30 ft. off the ground, is probably not much more than 5% or so of the front side irradiance.
By way of some explanation: A thought experiment: For hours of collection, say between 0900 and 1500 hrs. solar time, a good portion of the ground (the white concrete) surface that the underside of that array will "see" with more than a very small view factor will be the ground under the array, and thus (unfortunately) be shaded - and so not much to reflect there - only diffuse reflected, some of which was itself reflected before it got to the only reflecting surface with a decent view factor. The view factors for the rest of the surroundings - for walls, other nearby surrounding buildings (and probably not as white and therefore not as reflective) etc., will be quite small, the smallness of the view factors mostly due to the high angles of incidence of the other surfaces relative to the undersurface of the array. For the white concrete under the array, if it is shaded by the array, as it must be (for most of the time and mostly during peak sun hours), that means the only solar radiation incident on the concrete under most of the array will be diffuse, with the additional penalty (to reiterate) that most or all such diffuse radiation will be comprised mostly of backscattered diffuse radiation and diffuse radiation incident as a result of already having been reflected from other probably diffuse surfaces, perhaps multiple times, weakening and scattering more with each "re"-reflection.
Additionally, since it's highly likely that most or all of the small amount of solar radiation reaching the underside of the array will be diffuse, an additional penalty will be in place. Reason: transmittance of diffuse radiation through glazing is less than for beam radiation. This is due to the higher effective (averaged) angles of incidence of the scattered, diffused light, and how, because higher angles of incidence have greater surface reflectance, less radiation is present tor transmittance.The common approximation is to take the reflectance of diffuse radiation as being appox. the same as that of beam radiation at a 60 deg. incidence angle. For most transparent materials used in solar energy applications that translates into an approx. 10% additional penalty in collected energy. That's due to increased reflection of diffurse solar radiation only.
There is also a small additional penalty to be paid due to increased panel temp. This is small, but ought to be at least considered. Say the backside enhancement does amount to a 5 % increase in incident radiation. Since, at least to a pretty good 1st approx., and from energy (heat) balance considerations, that will increase the cell temperatures by something like ~ 5% over the not bifacial temp. diff between the array and the surroundings. That will mean something like a 1 C. or so increase in panel temp., resulting in another 0.5% or so decrease in energy collected due to temp. induced efficiency decrease. That needs to be taken as a reduction to my (assumed) 5 % enhancement from back face irradiation..
Now, If the design came in at the same price with or without bifacial panels, and assuming (somewhat generously I'd respectfully submit), O. & M. and other costs are the same, I'd say consider going for the bifacial option for this non residential option. However, given the dearth of knowledge surrounding how to estimate the potential enhancement to incident radiation on the backside of panels from reflection, I'd not go for it if it cost much more than the non bifacial option without some serious work.
I'd respectfully suggest to those who think large increases in incident radiation, and thus annual output are possible from the use of bifacial panels, to understand the possibilities and constraints that are part of the reality of the situation. Large (say~ > 10 % ) increases in actual yearly output without some compromises in aesthetics or some added costs in ancillary equipment or additional design requirements are probably hard to come by, and rarely cost effective in residential situations.
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